Theis, S. (2022) Offsetting approved harmful anthropogenic impacts in the 21st century – Insights into global offsetting practices, habitat banking as an alternative offsetting mechanism and application of habitat enhancement in northern boreal lake systems.

Thesis Title: Offsetting approved harmful anthropogenic impacts in the 21st century – Insights into global offsetting practices, habitat banking as an alternative offsetting mechanism and application of habitat enhancement in northern boreal lake systems.

Author: Sebastian Theis


Land-use change via human development is a major driver of biodiversity and habitat area loss and ecosystem function impairment. To reduce these impacts, billions of dollars are spent on environmental offsets, aimed to compensate for authorized negative impacts. Studies evaluating offset project effectiveness and individual mechanisms, remain rare.

Chapter 2 aimed to address the persistent questions of whether high project compliance is synonymous with high functional success as well as how to address residual or chronic impacts in aquatic ecosystems which can occur after offset establishment, for example because of the ephemeral timescale of some projects through a systematic review process and meta-analysis. While compliance and function were related to each other, a high compliance score did not guarantee a higher degree of function. However, function did improve with larger projects, specifically when projects targeted productivity or specific habitat features, and when multiple complementary management targets were in place. Altogether these relationships highlight specific ecological processes that may help improve offsetting outcomes for the conservation of habitat and biodiversity. The meta-analysis for offsetting residual or chronic impacts yielded three main approaches; habitat creation; restoration and enhancement and biological manipulation. Habitat creation projects, mainly targeting salmonids, with a high pooled effect size (0.8) and biomass increase (x1.4) needs to be explored for other species had a pooled effect size. Habitat restoration projects targeted a wide range of species and communities with a pooled effect size of 0.66, and intermediate biomass increases (>1x). Biological manipulation had the lowest effect size (0.51) with effort outcomes being highly variable.

Conservation and mitigation banks are widely used alternative mechanisms to traditional offsetting to compensate for unavoidable negative environmental impacts from development. In Chapter 3 we utilized publicly available banking data from for the United States to test whether area ratio requirements were met as well as how well ecological equivalency was achieved and to model current and future bank reserves through a predictive modeling framework. We conclude that most bank transactions using Preservation, Enhancement, and Re-establishment targeting wetlands, species, or multiple Mitigation-Targets met No Net Loss requirements on a ratio base. Wetland transactions, making up most of all assessed transactions (n = 10628), still missed matching appropriate impact to offset types in 25% of all cases, mainly due to Preservation not leading to any additional habitat area gain.  While the Preservation of wetlands and the Rehabilitation of streams can provide a multitude of benefits, both practices need to be revised on an ecological level to bridge the gap between Not Net Loss based on credit and area yield ratios and ecological equivalence. Future predictions indicate a decrease in available reserves for banks targeting wetlands or multiple ecosystems, with potential bottlenecks relating to large reserves being limited to the Southeast and release schedules not catching up to the current and anticipated demand. Banks targeting species or streams are predicted to meet future demand, with species banks (conservation banks) following a different legislative and operational approach based on the listing of endangered species. Most current reserves for all four bank types are restricted to very few service areas with around one-third of all bank areas still awaiting release, limiting their availability on a broader scale.

Chapter 4 focussed on the introduction of coarse woody habitat in a northern boreal lake and responses of aquatic fish, invertebrate and macrophyte communities through a Bayesian modeling approach and the use of changes in beta diversity components over time. Catch data was collected over 2 years and posterior model predictions showed an increase in habitat use of the enhanced areas by resident fish (spottail shiner – Notropis hudsonius; northern pike – Esox lucius; white sucker – Catostomus commersonii; brook stickleback – Culaea inconstans), while no probable effect on overall fish health, measured in Relative Weight, was linked to the enhancements. Enhancement structures featured increased macrophyte and invertebrate richness and biomass compared to reference sites and pre-treatment assessments over the course of three years. Enhanced sites also retained improved richness (macrophytes), diversity (macroinvertebrates) and biomass (both), despite structural integrity loss of enhancements as early as 1 week post construction.


Pallard, J. (2022) Assessing the effects of non-native salmonids on Bull Trout (Salvelinus confluentus) in Alberta’s Rocky Mountain foothills.

Thesis Title:Assessing the effects of non-native salmonids on Bull Trout (Salvelinus confluentus) in Alberta’s Rocky Mountain foothills.

Author: Jacqueline Pallard


The rapid decline in global biodiversity threatens the natural resources, food security, health, and livelihoods of current and future generations. Anthropogenic activities, including the introduction of non-native species, habitat fragmentation and alteration, and resource extraction, have exacerbated this decline. One such imperiled species are Bull Trout (Salvelinus confluentus), which have exhibited significant declines throughout their range and are expected to decline by >30% over the next 21 years in Alberta. While their decline is attributed to a myriad of threats, the degree to which non-native fishes contribute to their decline is uncertain. The objective of my thesis was to investigate the effects of Brook Trout (Salvelinus fontinalis) and Brown Trout (Salmo trutta), two non-native salmonids, on the habitat use and dietary niche of Bull Trout. To address the habitat component, I developed a multi-species N-mixture model using in-stream and land use derived characteristics to assess how Brook Trout and Brown Trout affect Bull Trout abundance in relation to habitat factors. I determined that Brook Trout negatively affect Bull Trout abundance when streams are <11°C and lack habitat complexity. Interactions between Brown Trout and Bull Trout are less certain, but larger, lower elevation streams are likely to see reductions in Bull Trout abundance where Brown Trout invasion is present and likely to occur. To address the dietary component, I employed stable isotope analysis to investigate how Brook Trout and Brown Trout interact with the dietary niche of Bull Trout. I determined that Bull Trout in sympatry with both Brook Trout and Brown Trout undergo a niche shift and are displaced from terrestrial-based resources. Furthermore, potential for competitive exclusion exists when resources are low given all species exhibit a high degree of niche overlap (>80%) when in sympatry and the amount of niche overlap does not decrease between allopatry and sympatry. The findings of my thesis suggest that both Brook Trout and Brown Trout interfere with the resource use of Bull Trout, on multiple levels, and provides practical guidelines for limiting future declines.


Roberts, K. N. (2022) The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Thesis Title: The structure and dynamics of fish isotopic and trophic niches in natural lakes and constructed fisheries offsets in the Alberta Oil Sands.

Author: Karling Roberts


Habitat offsets, where damages to natural ecosystems caused by socio-economic development projects are compensated for by the construction or restoration of ecosystems, can contribute to biological conservation when implemented properly. But, large uncertainties remain surrounding our ability to construct ecosystems that offer high quality habitat and sustainably provide desired ecosystem functions and services. Trophic structure and dynamics sustain ecosystem stability and function by limiting competition between consumers and alleviating prey species from damaging levels of predation. The application of food web theory has improved outcomes in ecological restoration and conservation, and has the potential to do the same for habitat offsetting. In this thesis I present one way trophic structure and seasonal trophic dynamics of an offset can be assessed, and examine how stable isotope analysis can be improved for use on sensitive species and in multi-season studies.

In the Alberta oil sands, unavoidable destruction of fish habitat from open-pit mining is offset with the construction of small lakes on or near mine sites. To investigate trophic structure in constructed offsets, I sampled the first offset lake constructed in the Alberta oil sands, Horizon Lake, and eight natural lakes for comparison. I measured stable carbon and nitrogen isotope ratios in the tissues of fish, and used these values to estimate metrics of trophic structure. I found that, despite the unique fish assemblage found in the offset lake, its trophic structure metrics are within the range of variation detected in natural lakes. The offset lake was most similar in terms of habitat to natural lakes that are relatively small and deep, but its trophic structure was more similar to large lakes with diverse fish assemblages. We recommend trophic structure continue to be examined in these and other offsets to further our understanding of their potentially unique ecology.

Seasonal variation in environmental conditions and resource availability may play an underappreciated role in the maintenance of biodiversity, especially in ecosystems that experience drastic seasonal changes. High-latitude and high-altitude aquatic ecosystems switch between an open water state in the summer and an ice covered state in the winter. This large environmental change is associated with reduced primary and secondary productivity, but it is not clear how consumers such as fishes respond. To address this knowledge gap, I examined the trophic dynamics of fish populations in three natural lakes and one constructed offset habitat. I used stable isotope analysis and stomach content analysis to assess if fish were 1) maintaining the same diet across seasons, 2) changing their diet seasonally, or 3) going dormant seasonally. We found that fishes most commonly change their diet between seasons in the three natural lakes and the offset. But, there was also evidence of diet maintenance and seasonal dormancy. Flexible foraging and a diversity of seasonal trophic responses among fish populations are likely contributing to the maintenance of biodiversity within these ecosystems. Evidence of winter activity by fishes in the offset is promising, and suggests the habitat is fulfilling its role as an over-wintering habitat for fishes.  

Stable isotope analysis is an important ecological method with many applications, but it often requires lethal sampling to obtain tissue samples. In addition, most stable isotope research is performed in the summer, leaving a gap in our understanding of whether isotope data collected in different seasons can be interpreted using the same methods. To address this, I investigated how lethal (muscle) and non-lethal (fin) tissues differ in their stable carbon and nitrogen isotope ratios, and whether inter-tissue differences change with season. I found that muscle and fin differ consistently in carbon and nitrogen stable isotope ratios, but whether season affects this relationship is species- and isotope-dependent. We recommend accounting for differences in tissue types whenever possible, and accounting for season of capture when research questions are highly sensitive to variation in isotope ratios.

Overall, this thesis demonstrates how ecological study of constructed offsets can advance our understanding of human modified ecosystems, basic ecological principles, and ecological methods. As offsetting grows as a practice across Canada and around the world, using these large-scale projects to further these objectives is imperative for improving the practice of offsetting and represents an enormous opportunity for advancing ecological research. 

Bazan, S. (2021) Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Thesis Title: Tubifex habitat analysis to assess whirling disease risk in Alberta, Canada.

Author: Sergio Bazan


During July 2021, 30 sampling sites at Bow River Watershed and 6 sampling sites at Crowsnest River were visited to perform tubifex relative abundance counts and the collection of environmental conditions associated to each site, such as stream characteristics, water physicochemical parameters, sediment composition and quality. Relative abundance of tubifex worms at Crowsnest River was significatively higher than any Hydrologic Unit 8 (HUC8) of Bow River Watershed except for Jumpingpound Creek (p-value 0.372). Higher relative abundance of tubifex worms were found in Jumpingpound Creek and Highwood River within Bow River watershed, but the difference with the other HUC8 was not statistically significant. The land use analysis results show higher relative abundance of tubifex worms around urban and farmland areas. However, the differences between all land use categories were not statistically significant (p-value 0.515), The same results were found for Silt-Clay type of sediments over of Granular sediments with no statistically significant difference (p-value 0.543). A multivariable linear model of tubifex relative abundance for the study area was built. The adjusted r-squared value was (R 2 = 0.1755). The variables included in the model were: the water pH, the wetted width, the stream velocity, the estimated flow, and the sediment classification. However, the assumption of linearity and homogeneity of variances were not meet by the proposed linear model.

Congratulations to Karling Roberts and Taylor Lund for their paper which was “Highly Commended” for the FSBI Huntingford Medal!

Congratulations to Karling Roberts and Taylor Lund, whose paper (citation below) was listed as one of two papers Highly Commended for FSBI Huntingford Medal!

  • Roberts, K.N., Lund, T., Hayden, B. and S. Poesch (2022) Season and species influence stable isotope ratios between lethally and non-lethally sampled tissues in freshwater fish. Journal of Fish Biology 100(1): 229-241. (link

Dutra, M.C.F., Pereyra, P.E.R., Hallwass, G., Poesch, M.S. and R.A.M. Silvano. (2023). Fishers’ knowledge on trophic ecology and of the tropical ‘super fish’ Plagioscion squamosissimus in two Brazilian Amazonian rivers. Neotropical Ichthyology 21(1): e220041.


Fishers’ local ecological knowledge (LEK) can provide new data on fish trophic ecology. The pescada (Plagioscion squamosissimus) is among the most caught fishes in small-scale fisheries in the Brazilian Amazon. Our main goal was to evaluate the abundance, size, relevance to small-scale fisheries and trophic ecology (diet and feeding interactions) of P. squamosissimus in the Tapajós and Tocantins rivers, in the Brazilian Amazon, utilizing  data from fishers’ LEK and fish sampling. We hypothesized a higher abundance, size and more prey and predators cited by fishers of P. squamosissimus in the more pristine Tapajós River. We interviewed 61 and 33 fishers and sampled fish in nine and five sites in the Tapajós and Tocantins Rivers, respectively, in 2018. The comparison between fishers’ citations and fish sampled indicated a higher relevance of P. squamosissimus to fishers in the Tapajós River, where this fish had an average larger size and where the interviewed fishers mentioned more food items of P. squamosissimus. These results show that P. squamosissimus is a generalist fish, that is resilient to fishing and environmental pressures, as well as being important to fisheries and food security, and that LEK can provide useful insights to fisheries managers. Keywords: Offsetting; Conservation policy; Biodiversity market; Preservation.

Citation: Dutra, M.C.F., Pereyra, P.E.R., Hallwass, G., Poesch, M.S. and R.A.M. Silvano. (2023). Fishers’ knowledge on trophic ecology and of the tropical ‘super fish’ Plagioscion squamosissimus in two Brazilian Amazonian rivers. Neotropical Ichthyology 21(1):e220041.

Also Read:

Pereyra, P.E.R, Hallwas, G., Poesch, M.S. and R. Silvano (2021) ‘Taking fishers’ knowledge to the lab’: an interdisciplinary approach to understand fish trophic relationships in the Brazilian Amazon. Frontiers in Ecology and Evolution.

*Lab members: Mark Poesch. Check out opportunities in the lab!